This invention relates to folding tools such as knives and multitools, and more specifically to a mechanism configured for firmly and safely retaining implements such as knife blades closed in the handle until a user intends the implements to be opened, and also for providing an opening assist for extending the implements into an open position for use.
Most folding knives and other folding tools include some kind of a mechanism that holds the blade or working implement safely in the closed position. In the case of knives, the blade is held in the closed position with the sharp cutting edge held safely within the handle. There are many, many known mechanisms for retaining blades in the closed position, and there are obvious reasons why such mechanisms are used. Among other reasons, blade-retaining mechanisms prevent unintended opening of the knife and thus promote safety. Even so, there are other reasons why most commercially available knives include devices that prevent unintended opening of the blade, and those include the need for compliance with applicable laws and regulations relating to knives that may be opened automatically. Nonetheless, safety considerations dictate that it is very important for a folding tool such a knife to include a mechanism that firmly and safely holds the blade in the closed position, and that the mechanism does not fail in any possible use situation.
Automatic opening mechanisms may be incorporated into folding knives and other folding tools, and there are many variations in what automatic opening mechanisms do, and how they function. Likewise, in appropriate circumstances and for appropriate users, there are many advantages to be derived from automatic or semi-automatic opening knives and many situations where automatic knives can be useful. These often include situations where the user has only one hand free. However, even in a knife that includes an automated opening or opening assist mechanism, safety considerations always mandate that the blade stays in the closed position until the user volitionally and intentionally moves the blade into the open position. For example, a mechanism that holds a knife blade closed should never release when the knife is dropped.
There is a need therefore for a mechanism that reliably retains the blade safely in the closed position, even in a knife that includes an automatic opening mechanism, and therefore eliminates the dangers inherently associated with a blade that could be opened either with a flick of the wrist, or inadvertently. There also is a need for mechanisms that safely maintains the blade in the closed position while providing opening assist functionality.
The present invention comprises a safety mechanism that may be incorporated in folding tools of all kinds, including knives and multitools and the like. With reference to a folding knife, the mechanism of the present invention preferably uses a liner spring to bias the blade into the closed position with the blade safely held in the knife body. The mechanism holds the knife blade firmly in this closed position until the user intentionally desires to open the knife. The blade cannot be moved into the open position with even an exceedingly strong xe2x80x9cflick of the wrist.xe2x80x9d Instead, the user must intentionally and volitionally begin rotating the blade from its closed position toward the open position, against the biasing force of the mechanism pushing the blade toward the closed position.
The present invention further may comprise a mechanism for providing opening assist functionality. Once a certain critical or xe2x80x9cthresholdxe2x80x9d point in the rotational movement is passed as the blade is moved from the closed toward the open position, the mechanism of the present invention rotationally drives the blade into the fully open position. This is accomplished by use of a spring mechanism that applies force to the blade, imparting sufficient rotational kinetic energy to the blade that the inertia drives the blade into the fully open position. A locking mechanism locks the blade in the open position.
To close the knife, the locking mechanism is released and the blade is rotated in the opposite directionxe2x80x94from open to closed. Once the blade is again moved past the critical point in the rotational movement, the actuating mechanism drives the blade back in the opposite directionxe2x80x94that is, into the closed position. By varying structural parameters, the amount of force applied to the blade in both the opening and closing direction may be varied and controlled. This can be of use when, for example, the manufacturer desires the closing force to be less than the opening force.
The actuating mechanism is in one preferred embodiment defined by a liner having a longitudinal slot cut therein and having an open end on the forward end of the knife body. The slot follows a specific path that at one point in a preferred embodiment is constricted and defines a top-dead-center point. This point in turn defines a threshold point, and is typically a generally V-shaped section of the slot.
The slotted liner thus defines a spring mechanism and the liner material on one side of the slot is a spring arm that exerts a biasing force on a cam pin extending from the tang of the blade, and which rides in the slot. When the blade is rotated about a blade pivot axis the pin likewise moves through an arcuate path, moving the pin longitudinally in the slot. As the pin moves longitudinally in the slot, the pin causes the spring arm defined by the liner material to lift, thereby exerting a biasing force on the cam pin, and thus on the knife blade. Depending upon which side of the threshold point the pin is on, the biasing force applied to the blade causes the blade to be forced in one of two directions (i.e., either toward the open position or toward the closed position).